Nanoscale Alloying, Phase-Segregation, and Core−Shell Evolution of Gold−Platinum Nanoparticles and Their Electrocatalytic Effect on Oxygen Reduction Reaction

Abstract

The design of active and robust bimetallic nanoparticle catalysts requires the control of the nanoscale alloying and phase-segregation structures and the correlation between the nanoscale phase structures and the catalytic properties. Here we describe new findings of a detailed investigation of such nanoscale phase structures and their structure-catalytic activity correlation for gold-platinum nanoparticles prepared with controllable sizes and compositions. The nanoscale alloying and phase-segregation were probed as a function of composition, size, and thermal treatment conditions using X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, electrochemical characterization, and density functional theory modeling. The results have provided the experimental evidence in support of the theoretically simulated dependence of alloying and phase segregation on particle size and temperature. More importantly, new insights have been gained into the control of the nanoscale phase properties of this bimetallic system among alloyed, partially alloyed, or partially phase segregated structures. In contrast to the largely alloyed character for the catalysts treated at 300-400°C, the higher-temperature treated catalysts (e.g., 800°C) are shown to consist of a Pt-rich alloy core and a Au shell or a phase-segregated Au domains enriched on the surface. This conclusion is further supported by the electrochemical and electrocatalytic data revealing that the catalytic activity is highly dependent on the nanoscale evolution of alloying and phase segregation. The thermal control of the nanoscale alloying, phase-segregation, and core-shell evolution of the nanoscale bimetallic catalysts provided the first example for establishing the correlation between the nanoscale phase structures and the electrocatalytic activity for oxygen reduction reaction correlation, which has profound implications to the design and nanoengineering of a wide variety of bimetallic or multimetallic nanostructures for advanced catalysts.

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

“…Upon addition of the support, the silica condensation with the MPTES carrying the metal ions would produce a good dispersion of both metals. During calcination, the gold strongly anchored to the silica surface would form a reverse core-shell structure with respect to that predicted by theoretical and experimental investigation [56,57]. In accord with the XPS Au/Pt atomic ratio and with the CO adsorption FTIR results, a structural change from a Pt core -AuPt shell like structure to a Au coreAuPt shell like structure is taking place by simply extending the time the two metal ions spend in solution with the MPTES ligand.…”

Nonstoichiometric Polyelectrolyte Complexes: Smart Nanoreactors for Alloy and Multimetallic Catalyst

“…4 shows STEM images and line-scan EDX spectra which exhibits an existence of individual Au, Ag, and PdNPs as separate entities rather than alloy or core-shell NPs. Also in some points, overlapped/ phase segregated structure of NPs within the PECs could be found [14]. Further confirmation was carried out from UV-vis measurement (Fig.…”

Nanoscale Alloying in Electrocatalysts

“…The size and composition of the nanoparticles produced by thermochemical processing are controllable. As shown for a series of binary and ternary alloy nanoparticle systems in Table 1 [12][13][14][15][16][17][23][24][25][26][27][28][29][30][31][32][33][34][35], the catalysts prepared by the molecularly-mediated synthesis and thermochemical processing methods have demonstrated enhanced catalytic and electrocatalytic properties for oxygen reduction reaction (ORR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR), etc. …”

“…A strong correlation between the size, structure and catalytic activities was revealed over several interesting systems, e.g., PtNi, PtCo and AuPt [12,13,23,27,28]. Gold-platinum (AuPt) nanoalloys serve as an intriguing system in terms of the unique synergistic properties [12,27,28].…”

“…The electrocatalytic ORR activities of AuPt nanoalloys have been assessed by rotating disk electrode (RDE) measurements [27]. As shown by RDE curves in Figure 3 for Au22Pt78/C and Au49Pt51/C catalysts, there are clear differences of the reduction currents in the kinetic region (0.8-0.9 V vs. NHE).…”